The present invention relates to a retention device for elements being part of and within a telescopically linked variable length device including the drive means for advancing and retracting these telescoping elements and cooperating with a spindle drive with nut elements traveling thereon as the spindle rotates, further including structure for positively connecting the elements in relation to each other upon deployment and extension.
Devices of the type to which the invention pertains include structures shown for example in German patent No. 26 03 488 and German printed patent application No. 31 16 770. Devices of the type generally to which the invention pertains exhibit a danger that upon protraction and deployment of the telescopic arrangement, friction establishes lateral loads on the telescoped element or elements so that as a result certain premature extension movement obtains even though a specific extension should not occur until adjacent elements have reached their maximum deployment tension. In other words, normal operation requires that one element after the other is caused to protract and the respective next one should begin to protract only after the respective preceding one has attained fully extended position. In the case of such premature extension the danger exists that friction interferes with the regular sequencing of deployment. In order to avoid this drawback it has been suggested to provide a spindle drive with an axial extension such that a nut of a telescopic element is always engaged and the telescopic elements have abutments in conjunction with a latching equipment to provide positive coupling in a predetermined sequence. This is basically shown in the German patent mentioned earlier, 26 03 488.
Another device has been proposed where latching and locking between elements obtains under utilization of mutual latch operation and coupling to enforce a particular sequence and a dependency upon relative positioning of the elements in relation to each other. This approach is shown in German printed patent application No. 31 16 770. Another possibility exists for retaining elements of a telescopic unit by providing bores in these elements to cooperate with pin locks.